The country also has 402 kilometers (249 miles) of coastline on the Bight of Biafra, part of the Atlantic Ocean. The topography of Cameroon is varied, ranging from tropical rain forests in the south to mountainous highlands in some western central regions, and semi-arid savanna in the far north.
The Ionisphere bounces radio waves back to earth and regulates the amount of radiation that gets to the lower atmospheres. It all depends on the Sun's activity. The stratosphere is what actually protects us from the UV rays of the sun.
One is because of what I described above; the wavelength is about the same as ordinary object. Radio waves tend to exhibit diffraction, that is they can bend around objects that are near the same size as their wavelength. So, radio waves can go around objects in general. The other way radio waves interact with objects is by reflection. Radio waves can bounce off objects. Often when radio waves hit an object like a building for example it will do both, refract around the building and reflect off of it as well. Now finally to your question. The main thing that makes radio waves go through an object or reflect off of it is the electromagnetic nature of object itself. Most common building materials like wood, plaster, glass, brick, stones, cement, etc are very poor conductors of electricity. These materials are referred to as dielectric materials.